Synchronization of clients to maximize multicast opportunities

ABSTRACT

A content monitor includes a processor that at least receives requests from a plurality of clients for content, instructs each client to retry their respective request at a first later time if the request is received before a first time, counts the requests to determine if a number of the requests exceeds a threshold if the request is received before a second time, instructs each client to retry their respective request at a second later time if the counted number of requests does not exceed a first threshold, instructs each client to join a multicast group to receive the content when the number of requests exceeds the first threshold, and counts a number of late clients joining the multicast group after a first portion of the content has been sent to the multicast group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/183,071 filed on Feb. 18, 2014, which is a continuation of U.S.patent application Ser. No. 13/404,946 filed on Feb. 24, 2012, now U.S.Pat. No. 8,656,042 which is a divisional of U.S. patent application Ser.No. 12/608,649 filed on Oct. 29, 2009, now U.S. Pat. No. 8,150,993, allof which are hereby incorporated by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to communications networks, andmore particularly relates to synchronization of clients to maximizemulticast opportunities.

BACKGROUND

Packet-switched networks, such as networks based on the TCP/IP protocolsuite, can distribute a rich array of digital content to a variety ofclient applications. One popular application is a personal computerbrowser for retrieving documents over the Internet written in theHypertext Markup Language (HTML). Frequently, these documents includeembedded content. Where once the digital content consisted primarily oftext and static images, digital content has grown to include audio andvideo content as well as dynamic content customized for an individualuser. Additionally, digital content can include updates such as softwareand programming updates.

Unicast protocols offer point-to-point communication between a serverand a client that can be used for delivering content. Unicastcommunications can be connection-oriented or connectionless. Forconnection-oriented unicast protocols, each request for content canresult in the establishment of a connection between the server and theclient. Maintaining the connection requires the server to dedicate theresources needed to provide the content to the client. Forconnectionless unicast communications, the server can send an amount ofdata towards the client without establishing a connection between theclient and the server. While a connectionless unicast communication canavoid the overhead of establishing the connection and the need toreserve resources for the connection, the connectionless unicastcommunication may not provide a mechanism for ensuring delivery of thecontent.

In contrast to unicast protocols, multicast protocols can allowsubstantially simultaneous distribution of digital content to a largenumber of clients without creating multiple point-to-point connections.The server can provide the content to a multicast group with each memberof the multicast group receiving a copy of the content at substantiallythe same time. Generally, multicast communications require networkresources to replicate the content as it traverses the network and tomaintain information regarding which clients are receiving the multicastcontent in order to ensure content is replicated throughout the networkcorrectly.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the Figures have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements. Embodiments incorporatingteachings of the present disclosure are shown and described with respectto the drawings presented herein, in which:

FIG. 1 is a block diagram illustrating a communications network inaccordance with one embodiment of the present disclosure;

FIG. 2 is a block diagram illustrating a system for providing content inaccordance with one embodiment of the present disclosure;

FIG. 3 is a flow diagram illustrating an exemplary method of providingcontent in accordance with one embodiment of the present disclosure;

FIG. 4 is a timing diagram illustrating delivery of content inaccordance with one embodiment of the present disclosure;

FIG. 5 is a flow diagram illustrating another exemplary method ofproviding content in accordance with one embodiment of the presentdisclosure;

FIG. 6 is a flow diagram illustrating an exemplary method of receivingcontent in accordance with one embodiment of the present disclosure; and

FIG. 7 is an illustrative embodiment of a general computer system.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION OF THE DRAWINGS

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferred exemplaryembodiments. However, it should be understood that this class ofembodiments provides only a few examples of the many advantageous usesof the innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily limit any ofthe various claimed inventions. Moreover, some statements may apply tosome inventive features but not to others.

FIG. 1 shows a multicast tree 100 for distributing digital contentthrough a geographically dispersed network, such as the Internet.Multicast tree 100 can include a server 102 and client systems 104through 118. Server 102 and client systems 104 through 118 cancommunicate through a network of distribution points 120 through 130.The distribution points 120 through 130 may be routers. Alternatively,the distribution points 120 through 130 may be nodes of an overlaynetwork. For example, communication from server 102 can travel throughdistribution points 120, 124, and 126 to client system 108 whilecommunication from server 102 can travel through distribution points 120and 130 to client 116. It will be appreciated that multicast tree 100may be a logical overlay of a mesh network that, for example, may have adirect connection from distribution point 130 to 128, and also, forexample, may have a direct connection from distribution point 126 to130. These distribution points may be multicast-enabled routers. Thedistribution points may have the ability to cache content not only forimmediate forwarding but also for later retransmission. In anembodiment, the server 102 can be a distribution node or edge server ofa content delivery network. As such, the server 102 can receive digitalcontent for distribution from an origin server.

Server 102 can use Internet Protocol (IP) multicast or any othermulticast protocol to substantially simultaneously distribute digitalcontent, such as a software update, to the client systems 104 through118. The data file can be divided into multiple segments or data packetsthat may be, but are not necessarily IP packets, Ethernet frames, orsimilar lower layer packets. Using a multicast protocol, each suchsegment or data packet can move over each link of the network only once.The distribution points 120 through 130 can create copies, or otherwiseforward incoming data on one port to multiple outbound ports, when thepaths to the destinations split. For example, server 102 can send amulticast data packet to distribution point 120. Distribution point 120can send a copy of the data packet to each of client 104, distributionpoint 124, and distribution point 130. Similarly, distribution point 130can send, forward, or route, a copy of the segment, data packet, orindividual low layer packets to each of client systems 116 and 118, anddistribution point 124 can send a copy of the data packet to each ofdistribution points 126 and 128. Further, distribution point 126 cansend a copy of the data packet to each of client systems 106 and 108 anddistribution point 128 can send a copy of the data packet to each ofclient systems 110, 112, and 114. In other embodiments, the networkunderlying multicast tree 100 may be a shared medium, such as a bus orring, with multicast occurring at a low network layer via commonphysical components and a common media access structure.

Generally, the distribution points construct the multicast tree 100 whenclient systems join a multicast group, and the server 102 may not haveinformation about each member of the multicast group. Specifically,client systems can notify the network that they are interested inreceiving data packets sent to the multicast group, such as by InternetGroup Management Protocol. The server 102 can send a message addressedto the multicast group and each distribution point can replicate thedata packet for each system of the multicast group.

The multicast tree 100 can include five multicast subtrees, each definedby a respective root node coupled with a path to the root node from theorigin server 102. For example, there is a subtree comprisingdistribution node 126 as well as endpoints 106 and 108, coupled withpath 102-120-124-126. There is also a subtree rooted at node 124,further comprising nodes 126 and 128 and endpoints 106 through 114,coupled with path 102-120-124.

There may be significant differences between the total costs fordelivering content using unicast versus delivering content usingmulticast. For unicast delivery, there is a server cost associated withdelivering the content to each client that requests it. The server costcan include memory utilization, CPU utilization, bandwidth utilization,and the like. For connection-oriented unicast delivery, there is a costassociated with each connection to a client. The available bandwidth,processing power, memory, number of processes, and number of connectionscan limit the number of clients that the server can serve concurrently.In addition to the server cost, there is a network cost associated withproviding the content. Each router along the network path between theclient and server can utilize resources for routing, buffering, andforwarding the content. Further, error detection and correction canimpose costs on the server, such as parity calculations, and thenetwork, such as an increased number of bits. The error detection andcorrection costs may be different for connection-oriented unicast thanfor connectionless unicast. Additionally, the connection between theserver and the client requires a portion of the available bandwidth foreach link along the network path. When providing the content to a largenumber of clients, the overall cost increases proportionally to thenumber of clients, as each point-to-point connection has a similar totalcost. Additionally, when the clients are dispersed throughout thenetwork, the costs impact the server and the network adjacent to theserver more significantly than other portions of the network.

For multicast content delivery, the server only provides one datastream. Accordingly, the server cost is substantially fixed for apotentially unlimited number of clients, significantly reducing theserver cost compared to unicast when serving a number of clients.Additionally, the costs associated with error correction and detectioncan be different for multicast transmission than for unicasttransmission. Further, the content may traverse each link in the networkonly once, significantly reducing the network utilization of linkshaving a large number of downstream clients. However, multicastdistribution can require additional resources from each distributionpoint or router within the multicast tree. The distribution points ofthe multicast tree may need to maintain a list of downstream devicesthat are part of the tree, track the downstream devices as they join orleave the multicast tree, and duplicate the network traffic to each ofthe downstream devices. Because the content is duplicated within thenetwork, the total cost can be distributed more evenly throughout thenetwork when delivering content to a large number of clients.Specifically, the costs nearest to the server can be substantiallyfixed, even through the number of clients may increase dramatically.

Generally, for a single client, unicast delivery has a lower cost thanmulticast delivery. However, once the number of clients exceeds athreshold, multicast delivery can be a significantly more efficient wayto deliver the content. Further, unicast delivery can provide content tomultiple clients that request content at slightly different times,whereas multicast delivery requires the coordination of the clientrequests because the content is simultaneously sent to all the clients.Efficient delivery of content can require determining if the number ofclients exceeds the threshold and coordinating the requests of theclients, such that a single multicast can serve a large number ofclients.

FIG. 2 illustrates an exemplary system for delivery of content,generally designated 200. The system can include a content monitormodule 202, a unicast content delivery module 204, and a multicastcontent delivery module 206. The content monitor module 202, the unicastcontent delivery module 204, and the multicast content delivery module206 can be implemented in hardware, software, or any combinationthereof. Each module may include one or more computer systems. When amodule includes more than one computer system, the functions of themodule can be distributed across the multiple computer systems in asymmetric manner, that is, each computer system performs the same typeof tasks, or in an asymmetric manner, that is, two computer systems ofthe module may perform different tasks.

Client system 208 can communicate with the system 200 through a network210. Client system 208 can send a request for content to the contentmonitor module 202 to determine if new or updated content is available.The content may be content that need not be delivered on demand, such asperiodic updates to software. Additionally, the content may be audio orvideo content that is prefetched and stored on a client system. Furtherexamples can include data sets that are periodically updated andsubscriptions to information feeds that are updated periodically. Thecontent monitor module 202 can count the number of clients makingrequests for a specific content item. Additionally, the content monitormodule 202 can respond to a request from the client system 208 with aninstruction to repeat the request at a specified later time, aninstruction to retrieve available content from the multicast deliverymodule 206, optionally specifying a time in the future at which themulticast delivery will begin, or an instruction to retrieve the contentfrom the unicast content delivery module 204. When a sufficient numberof client systems are requesting the same content, the content monitormodule 202 can instruct the client system 208 to retrieve the contentfrom the multicast content delivery module 206 to reduce the costsassociated with content delivery. Alternatively, when a small number ofclient systems are requesting the same content, it may be more efficientto deliver the content using unicast and the client system 208 can beinstructed to retrieve the content from the unicast content deliverymodule 204.

In an embodiment, the client system may periodically send a request tothe content delivery system to determine when new or updated contentbecomes available and the content delivery system may receive new orupdated content prior to the content being available to the clientsystem. For example, the content delivery system may receive a softwareupdate along with a time for the software update to be made available toclient systems.

FIG. 3 illustrates an exemplary method of delivering content. At 302, acontent delivery system, such as content delivery system 200, canreceive a request from a client system, such as client system 208. At304, the content delivery system can determine if the current time isafter a first specified time. The first specified time could be a firstnumber of seconds or minutes prior to when the content can be madeavailable to the client system. If the current time is not after thefirst specified time, the content delivery system can notify the clientsystem to try again after the first specified time, as illustrated at306. At 302, the content delivery system can receive another request.

In an embodiment, the content delivery system can determine a number ofminutes until the first specified time period and notify the clientsystem to try again after the determined number of minutes. For example,the first specified time can be about two minutes prior to when thecontent can be made available, although shorter or longer time periodsare contemplated. If the current time is more than two minutes prior towhen the content can be made available, the content delivery system candetermine the number of minutes (Y) between the current time (C) and twominutes prior to the content being made available (T−2), Y=T−2−C. Thecontent delivery system can notify the client system to try again in Yminutes.

Returning to 304, when the current time is after the first specifiedtime, the content delivery system can determine if the current time isafter a second specified time, as illustrated at 308. The secondspecified time could be a second number of seconds or minutes prior towhen the content can be made available to the client system. The secondnumber of seconds or minutes can be less than the first number ofseconds or minutes. If the current time is not after the secondspecified time, the content delivery system can increase a count of therequests received for the content within the second specified time, asillustrated at 310, and the content delivery system can notify theclient system to try again after the second specified time, asillustrated at 312. At 302, the content delivery system can receiveanother request.

In an embodiment, the content delivery system can determine a number ofminutes until the second specified time and notify the client system totry again after the determined number of minutes. For example, thesecond specified time can be about one minute prior to when the contentcan be made available to the client system, although shorter or longertime periods are contemplated. If the current time is before one minuteprior to when the content can be made available to the client system,the content delivery system can determine the number of minutes (Y)between the current time (C) and one minute prior to the content beingmade available (T−1), Y=T−1−C, and notify the client to try again in Yminutes.

Returning to 308, when the current time is after the second specifiedtime, the content delivery system can determine if sufficient requestshave been received to make multicast delivery more efficient thanunicast delivery, as illustrated at 314. Multicast delivery can be moreefficient than unicast delivery when the total cost of delivering thecontent to all of the requesting clients using multicast is less thanthe total cost of delivering the content to all of the requestingclients using unicast. The total cost can include server cost, networkcost, router cost, or any combination thereof. When there are asufficient number of requests, the content delivery system can instructthe client system to join a multicast session to retrieve the content,as illustrated at 316, and the content delivery system can receiveanother request at 302. Alternatively, when there is not a sufficientnumber of requests, the content delivery system can instruct the clientsystem to request unicast delivery of the content, as illustrated at318, and the content delivery system can receive another request at 302.

FIG. 4 shows a timeline illustrating the delivery of content. At 402,the client system can send a request for content to the content deliverysystem. At 404, the content delivery system can instruct the clientsystem to try again between T−2 and T−1. At 406, the client system cansend a request to the content delivery system. At 408, the contentdelivery system can count the request and notify the client system totry again in one minute, between T−1 and T. At about T−1, the contentdelivery system can determine that the number of requests exceeds athreshold such that multicast content delivery can be more efficientthat unicast content delivery. At 410, the client system can send arequest to the content delivery system. At 412, the content deliverysystem can notify the client to join a multicast group to receive theupdated content. The client system can join the multicast group and atabout T, and the content delivery system can begin a multicastdistribution of the content to the client system, as illustrated at 414.

FIG. 5 illustrates another exemplary method of delivering content. At502, a content distribution system, such as content distribution system200, can receive a request for content currently being distributed usingmulticast. At 504, the content distribution system can determine if themulticast has been recently started. When the multicast has beenrecently started, the client system can join the multicast to receive alater portion of the content and retrieve an earlier portion of thecontent separately. For example, the client system can receive anearlier portion of the content using unicast distribution eitherconcurrently with the multicast distribution or after the multicastdistribution has ended. Alternatively, the client system can join thecurrent multicast to receive the later portion of the content and join asecond multicast to receive the earlier portion of the content.

Determining whether a multicast session has been recently started maydepend on how the client system should receive the earlier portion ofthe content. When the earlier portion of the content should be retrievedusing a unicast protocol, a relatively small earlier portion may bedesirable, resulting in a relative short time period for a multicastsession to be considered recently started. Alternatively, when theearlier portion should be retrieved using a multicast protocol, arelatively large earlier portion may also be acceptable and themulticast session may be considered recently started as long as thelater portion is sufficient to justify the cost of joining the currentmulticast group instead of waiting for a later multicast group. In anembodiment, the number of clients waiting to join a multicast group forthe content may be used to determine if the multicast session has beenrecently started. For example, once a sufficient number of clientsystems have joined a multicast group late to justify multicast deliveryof the earlier portion, additional clients may be instructed to wait tojoin the next multicast session of the content.

When the multicast session has not been recently started, the contentdelivery system can increase a count of clients waiting for content, asillustrated at 506, and instruct the clients to retry shortly before thestart of the next multicast session, as illustrated at 508. Because thecount of clients waiting for content is being tracked, the contentdelivery system may not need to count the clients again beforedetermining if multicast delivery of the content is more efficient.Alternatively, the content delivery system may not count the number ofclients waiting for the content and instead count the clients when theytry again.

Returning to 504, when the multicast session has been recently started,the content distribution system can instruct the client system to jointhe multicast group, as illustrated at 510. Preferably, a client can beinstructed to join the existing multicast session unless the multicastsession may end prior to the client joining. Additionally, the contentdistribution system can count the number of clients joining themulticast group late in order to determine if there is a sufficientnumber of systems to justify utilizing a multicast protocol todistribute the earlier portion of the content. In an embodiment, thecontent distribution system can instruct client systems to join a newmulticast to receive the earlier portion of the content or extend themulticast session to provide the earlier portion of the content whenthere is a sufficient number of systems to justify utilizing a multicastprotocol to distribute the earlier portion of the content.

In an exemplary embodiment, the content distribution system can trackwhen client systems join the existing multicast session to estimate asize of the earlier portion of the content needed by each client systemjoining the existing multicast system. In addition to the number ofclient systems, the determination to use a multicast session to providethe earlier portion of the content can include information about theamount of content needed by each of the client systems. For example, thecost savings for adding an additional client to a multicast may beweighted by the amount of content needed by the client.

FIG. 6 illustrates an exemplary embodiment of a method of receivingcontent. At 602, the client system can send a request for content to acontent delivery system, such as content delivery system 200. At 604,the client system can determine if instructions received from thecontent delivery system indicate that the client system should try againlater. When the instructions indicate that the client system should tryagain, the client system can start a timer, as illustrated at 606. Thetimer can count down a number of minutes or seconds and the clientsystem can send a request at 602 after the timer has reached the numberof minutes or seconds.

Returning to 604, when the instructions do not indicate that the clientsystem should try again later, the client system can determine if theinstructions indicate that the client system should join a multicastgroup to receive the content, as illustrated at 608. If the instructionsdo not indicate that the client system should join a multicast group,the client system can retrieve the content using a unicast connection,as illustrated at 610. Once the content has been received, the processcan end at 612.

Alternatively, when the instructions indicate that the client systemshould join a multicast group, the client system can join the multicastgroup, as illustrated at 614. Once the content delivery system hascompleted sending the content to the multicast group, the client systemcan determine if the content is complete, as illustrated at 616. Thecontent may not be complete if the client system joined the multicastgroup late or if portions of the content were lost due to networkerrors. When the content is not complete, the client system can send arequest for the missing portion of the content, as illustrated at 602.Alternatively, at 612, when the content is complete, the process canend.

FIG. 7 shows an illustrative embodiment of a general computer system700. The computer system 700 can include a set of instructions that canbe executed to cause the computer system to perform any one or more ofthe methods or computer based functions disclosed herein. The computersystem 700 may operate as a standalone device or may be connected, suchas by using a network, to other computer systems or peripheral devices.Examples of the general computer system can include server 102,distribution point 120, client system 104, any computer system componentof content monitor module 202, unicast content delivery module 204, ormulticast content delivery module 206, and the like.

In a networked deployment, the computer system may operate in thecapacity of a server or as a client user computer in a server-clientuser network environment, or as a peer computer system in a peer-to-peer(or distributed) network environment. The computer system 700 can alsobe implemented as or incorporated into various devices, such as apersonal computer (PC), a tablet PC, an STB, a personal digitalassistant (PDA), a mobile device, a palmtop computer, a laptop computer,a desktop computer, a communications device, a wireless telephone, aland-line telephone, a control system, a camera, a scanner, a facsimilemachine, a printer, a pager, a personal trusted device, a web appliance,a network router, switch or bridge, or any other machine capable ofexecuting a set of instructions (sequential or otherwise) that specifyactions to be taken by that machine. In a particular embodiment, thecomputer system 700 can be implemented using electronic devices thatprovide voice, video or data communication. Further, while a singlecomputer system 700 is illustrated, the term “system” shall also betaken to include any collection of systems or sub-systems thatindividually or jointly execute a set, or multiple sets, of instructionsto perform one or more computer functions.

The computer system 700 may include a processor 702, such as a centralprocessing unit (CPU), a graphics processing unit (GPU), or both.Moreover, the computer system 700 can include a main memory 704 and astatic memory 706 that can communicate with each other via a bus 708. Asshown, the computer system 700 may further include a video display unit710 such as a liquid crystal display (LCD), an organic light emittingdiode (OLED), a flat panel display, a solid-state display, or a cathoderay tube (CRT). Additionally, the computer system 700 may include aninput device 712 such as a keyboard, and a cursor control device 714such as a mouse. Alternatively, input device 712 and cursor controldevice 714 can be combined in a touchpad or touch sensitive screen. Thecomputer system 700 can also include a disk drive unit 716, a signalgeneration device 718 such as a speaker or remote control, and a networkinterface device 720 to communicate with a network 726. In a particularembodiment, the disk drive unit 716 may include a computer-readablemedium 722 in which one or more sets of instructions 724, such assoftware, can be embedded. Further, the instructions 724 may embody oneor more of the methods or logic as described herein. In a particularembodiment, the instructions 724 may reside completely, or at leastpartially, within the main memory 704, the static memory 706, and/orwithin the processor 702 during execution by the computer system 700.The main memory 704 and the processor 702 also may includecomputer-readable media.

The illustrations of the embodiments described herein are intended toprovide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherembodiments may be apparent to those of skill in the art upon reviewingthe disclosure. Other embodiments may be utilized and derived from thedisclosure, such that structural and logical substitutions and changesmay be made without departing from the scope of the disclosure.Additionally, the illustrations are merely representational and may notbe drawn to scale. Certain proportions within the illustrations may beexaggerated, while other proportions may be minimized. Accordingly, thedisclosure and the FIGS. are to be regarded as illustrative rather thanrestrictive.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b) and is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing Detailed Description of the Drawings, variousfeatures may be grouped together or described in a single embodiment forthe purpose of streamlining the disclosure. This disclosure is not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter may bedirected to less than all of the features of any of the disclosedembodiments. Thus, the following claims are incorporated into theDetailed Description of the Drawings, with each claim standing on itsown as defining separately claimed subject matter.

The above disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosed subject matter. Thus, tothe maximum extent allowed by law, the scope of the present disclosedsubject matter is to be determined by the broadest permissibleinterpretation of the following claims and their equivalents, and shallnot be restricted or limited by the foregoing detailed description.

What is claimed is:
 1. A system, comprising: a memory that storesinstructions; a processor that executes the instructions to performoperations, the operations comprising: instructing, if a quantity ofrequests for content is determined to exceed a first threshold, each ofa plurality of client systems to join a multicast group to receive thecontent; and determining, based on determining a number of clientsystems waiting to join the multicast group, if a first multicastsession associated with the multicast group has been started within aperiod of time.
 2. The system of claim 1, wherein the operations furthercomprise counting the requests for the content to determine if thequantity of the requests for the content exceeds the first threshold. 3.The system of claim 1, wherein the operations further comprise countinga number of late client systems joining the multicast group after afirst portion of the content has been sent to the multicast group. 4.The system of claim 1, wherein the operations further comprisetransmitting, to a first client system of the client systems, a set ofinstructions that indicate that the first client system should requestthe content again.
 5. The system of claim 1, wherein the operationsfurther comprise increasing a count of client systems waiting for thecontent when the first multicast session associated with the multicastgroup has been determined to not be started within the period of time.6. The system of claim 1, wherein the operations further comprisetracking when each client system joins the first multicast session toestimate a size of a first portion of the content.
 7. The system ofclaim 1, wherein the operations further comprise instructing, if thequantity of the requests for the content is determined to not exceed thefirst threshold, each of the plurality of client systems to receive thecontent via unicast delivery.
 8. The system of claim 1, wherein theoperations further comprise enabling a portion of the plurality ofclient systems to obtain a first portion of the content via unicastdelivery and a second portion of the content via the first multicastsession.
 9. The system of claim 1, wherein the operations furthercomprise distributing a second portion of the content to late clientsystems in a second multicast session if the first multicast sessionassociated with the multicast group has been determined to have beenstarted within the period of time and if a first portion of the contenthas already been distributed via the first multicast session.
 10. Thesystem of claim 1, wherein the operations further comprise determiningan amount of the content to be distributed to each of the clientsystems.
 11. A method, comprising: instructing, if a quantity ofrequests for content is determined to exceed a first threshold, each ofa plurality of client systems to join a multicast group to receive thecontent; and determining, based on determining a number of clientsystems waiting to join the multicast group and by utilizinginstructions from a memory that are executed by a processor, if a firstmulticast session associated with the multicast group has been startedwithin a period of time.
 12. The method of claim 11, further comprisingcounting the requests for the content to determine if the quantity ofthe requests for the content exceeds the first threshold.
 13. The methodof claim 11, further comprising counting a number of late client systemsjoining the multicast group after a first portion of the content hasbeen sent to the multicast group.
 14. The method of claim 11, furthercomprising transmitting, to a first client system of the client systems,a set of instructions that indicate that the first client system shouldrequest the content again.
 15. The method of claim 11, furthercomprising increasing a count of client systems waiting for the contentwhen the first multicast session associated with the multicast group hasbeen determined to not be started within the period of time.
 16. Themethod of claim 11, further comprising tracking when each client systemjoins the first multicast session to estimate a size of a first portionof the content.
 17. The method of claim 11, further comprisinginstructing, if the quantity of the requests for the content isdetermined to not exceed the first threshold, each of the plurality ofclient systems to receive the content via unicast delivery.
 18. Themethod of claim 11, further comprising enabling a portion of theplurality of client systems to obtain a first portion of the content viaunicast delivery and a second portion of the content via the firstmulticast session.
 19. The method of claim 11, further comprisingdistributing a second portion of the content to late client systems in asecond multicast session if the first multicast session associated withthe multicast group has been determined to have been started within theperiod of time and if a first portion of the content has already beendistributed via the first multicast session.
 20. A computer-readabledevice comprising instructions, which when loaded and executed by aprocessor, cause the processor to perform operations, the operationscomprising: instructing, if a quantity of requests for content isdetermined to exceed a first threshold, each of a plurality of clientsystems to join a multicast group to receive the content; anddetermining, based on determining a number of client systems waiting tojoin the multicast group, if a first multicast session associated withthe multicast group has been started within a period of time.